Published U.S. Pat. No. 7,710,045B2 discloses an illumination assembly comprising a plurality of Light Emitting Diode (LEDs) dies. The illumination assembly comprises a substrate which comprises a first electrically conductive layer, a layer of an electrically insulating material which comprises thermal conductive particles, and a second layer of an electrically conductive material. The first electrically conductive layer is a patterned layer thereby forming a plurality of metal tracks acting as current conductors. In one embodiment, a bottom surface of the LED dies are electrically and thermally coupled to a single metal track of the first electrically conductive layer and are electrically coupled to another metal track with a wire bond that is coupled to a top surface of the LED dies. Wire bonds are relatively small and do not conduct heat well. In another embodiment, the LED dies have at one surface two areas for being coupled to an electrical source, and these two areas are electrically and thermally coupled to two different metal tracks of the first electrically conductive layer. The thermal coupling of LED dies to metal tracks of the first electrically conductive layer allows the heat generated in the LED dies to be transferred to the first electrically conductive layer. The layer of the electrically insulating material, which comprises thermal conductive particles, transfers a significant portion of the heat towards the second layer of electrically conductive material. The second layer of the electrically conductive material may be a metal, which is a thermal conductor. The second layer may be used to couple the illumination assembly to a heat sink. If no heat sink is coupled to the second layer of the electrically conductive material, the second layer transfers heat to the ambient of the lighting assembly.
The transport of heat from the LED dies towards the ambient and/or a heat sink being coupled to the second layer is not high enough for all applications, especially not when high power LEDs are used.